Abstract: During the construction of a pile foundation, the initial-pressure pile pressing exerts shading effects on the post-pressure pile, and the post-pressure pile displaces and compacts the surrounding soil, causing the initial-pressure pile to float and tilt. These combined effects affect the bearing capacity and stability of the pile foundation. Therefore, it is of great engineering significance to study the shading effect of the piles during soil displacement. Model testing and digital image correlation (DIC) technology were used to investigate the effect of the initial-pressure pile on the post-pressure pile, varying parameters including pile spacing, sand and soil grain size, and pile body roughness. Through an examination of the horizontal displacement of the soil around the initial-pressure pile during the sinking of the post-pressure pile, a reduction was observed in the horizontal the shading effect with increasing pile spacing. By fitting the horizontal attenuation amplitude for various pile spacings, it was inferred that when the pile spacing reaches 6D (D=30 mm), there was basically no shading effect of the initial-pressure pile on the postpressure pile. Varying the soil grain size had no significant impact on the horizontal shading effect of neighboring piles. However, the attenuation amplitude decreased as the pile body roughness decreased, indicating that smoother pile body resulted in smaller shading effects. As the post-pressure pile exerted pressure on the initial-pressure pile, the initial-pressure pile experienced tilting and uplifting. In conclusion, the smaller the pile spacing and the rougher the pile body, the larger the horizontal displacement, tilt angle, and uplift effect on the initial-pressure pile. Moreover, the finer the grain size of the soil around the pile, the smaller the horizontal displacement and uplift effect on the initial-pressure pile, but the larger the tilt angle it experienced.

Key words: digital image correlation (DIC) technology, model test, horizontal displacement, masking effect